1.Field of the Invention
This invention relates to circuit board heat dissipation and more specifically, relates to the use of solder paste to spread and dissipate heat on a circuit board.
2.Description of the Art
A substantial issue facing circuit board designers is the ability to efficiently dissipate/remove the heat generated by the circuit board devices to the surrounding area. For example, with respect to power circuits, the more efficiently the heat is removed, the more power that can be dissipated for a given rise in device junction temperature. One method designers currently use to remove the heat generated by devices is to dump the heat into the circuit board on which the devices are mounted and to thereafter use the larger surface area of the circuit board to dissipate the heat to the surrounding area. Nonetheless, this method of heat dissipation has several limitations.
First, as is readily understood, as the size of a circuit board increases, the exposed surface area of the circuit board also increases, thereby allowing for greater heat dissipation to the surrounding area. Accordingly, a circuit board is often sized to obtain adequate heat dissipation for the devices mounted thereon. However, at times, cost and space restrictions may prevent a circuit board from being adequately sized to obtain the necessary heat dissipation, even through only a small amount of additional surface area may be needed. In these cases, additional heatsinking and/or forced-air cooling may be required, both of which can be costly.
A second limitation with using a circuit board to dissipate heat is that the heat may not spread evenly across the circuit board, thereby causing the heat to not efficiently dissipate and resulting in the formation of hot spots on the board around hot devices. In order to prevent the formation of hot spots and to spread heat away from hot devices and across the circuit board, the copper weight of the top, bottom, and/or intermediate copper traces of the circuit board may be increased or the width of the copper traces on the surface of the circuit board may be increased. In general, each of these methods increases the cross-sectional area of the traces, thereby improving the ability of the traces to conduct heat away from the devices. In many cases, however, it is not possible to increase the weight and/or width of the traces.
For example, the motherboards found in notebook computers typically use only one-ounce copper traces on the surface of the boards. However, one-ounce copper traces are not sufficient for spreading heat away from power devices, for example. Accordingly, thick copper traces are required in the areas surrounding the power devices. However, increasing the copper weight of the traces around the power devices also means increasing the copper weight of the traces across the whole motherboard, even in areas where increased-weight traces may not be needed. Accordingly, this method adds additional cost, which may be prohibitive.
Accordingly, it is desirable to provide a mechanism that allows for improved heat spreading along a circuit board and away from hot devices and that allows for improved heat dissipation from the circuit board to the surrounding area.